I think they were made by Norma.
I had to redo a Husqvqrna 4 wheel steer last year and it ended being Norma .
Go to the Stens , or Rotary web catalogue and search Mandrels.
Should bring up a 100 or so images then go through & find one that looks the same as yours.
An old mum & pop repair shop will probably know what you are talking about but a glass front will just say "NLA here buy this nice new mower".